Variable pitch reversible propeller



April 22, 1952 E. H. MORRIS EFAL 2,593,910

VARIABLE PITCH REVERSIBLE PROPELLER Filed Aug. 30, 1948 2 SHEETS-SHEET 1Invento r s EDWARD H. MORRIS, ELLIS DANVERS & THOMAS E. GODDEN AttorneysApril 22, 1952 E. H. MORRIS ETAL 2,593,910

VARIABLE PITCH REVERSIBLE PROPELLER Filed Aug. 30, 1948 2 SHEETS-SHEET 2Fig.3.

Inventor s EDWARD H. MORRIS,

ELLIS DANVERS & THOMAS E. GODDEN Attorneys Patented Apr. 22, 1952VARIABLE PITCH REVERSIBLE PROPELLER Edward Hollingworth Morris, Ashtead,EllisDanvers, Gloucester, and Thomas Edward Godden, Cheltenham, England,assignors to Rotol Lim ited, Gloucester, England, a British companyApplication August 30, 1948, Serial No. 46,874, In Great BritainSeptember 2, 1947 Claims.

This invention concern variable-pitchpropellers of the kind in which theblades are capable of adjustment from a positive angle (to provideforward, thrust) to anegative angle (to provide backward thrust). Suchpropellers will be referred to as reversible pitch propellers.

Reversible pitch propeller are normally required to providebackwardthrustonly when the aeroplane is landing and the presentinvention has for its object to provide a system of control forpropellers of the kindreferred to in which the backward thrust isobtainable only after the aeroplane has touched down.

According to the present invention a reversiblepitch propeller comprisesa constant-speed unit for controlling the pitch of, the blades of thepropeller, means to over-ride said unit and brin the blades to withinthe negative pitch-range and means for bringing said over-riding meansinto operation only whilst the aeroplane is on the ground.

According to one feature of thisinvention a reversible-pitch propellercomprises a constantspeedunit for controlling the pitch of the bladesofthe. propeller, electrical means to over-ride said unit and bring theblades to within the negative pitch-range and switch means, in thecircuit of said electrical means, to control its operation, said switchbeing actuated to bring the electrical means into operation bythe weightof the aeroplane.

According to another feature of the invention a reversible-pitchpropeller comprises a hydraulic pitchechange motor, a constant-speedunitto control, the blade movements in the positive and negative pitchranges, means for over-riding the constant speed unit to move the bladesfrom one pitch rangeto the other, an electrical control for saidover-riding means and a switch for controlling the operation of saidelectrical control, said switch being actuated by the weight of theaeroplane.

Preierably said switch is actuated to bring the electrical over-ridingcontrol into operation by telescoping of the undercarriage of theaeroplane onlanding.

In order thatthe nature of the invention may be more clearly understooda practical application of it will now be described, by way of eX-ample, with reference to the accompanying drawings whereof:

Figure 1 is a side elevation of an aeroplane shown as it is coming intoland,,the aeroplane ,incorporatingpropellers in accordance with thisinvention,

Figure 2 is a schematic representation of the propellers of theaeroplane of Figure 1,

Figure 3 is a circuit diagram of the control system for the propeller ofFigure 2, and

Figure 4 is aschematic view of the engine-propeller assembly and of themain controls therefor.

In Figure-1 the aeroplane I00 has a pair of propellers 5 (one only ofwhichis seen in the drawings) which are driven, one each, by an enginecarried within the nacelle NH. The. aeroplane carries a rectractableundercarriage I 0.2! comprising, in known manner two telescoping legmembers I03, I04.

Each propeller 5 is hydraulically operated and is provided, in knownmanner, with a pitchchange motor 6 (see Figure 2) the ram 1 of which iconnected with the individual propeller. blades 8 by means of a linkage9.

Hydraulic fluid for the. operation of themotor 6 is provided by a pumpI04 which supplies fluid to the valve I05 of a constant speed unit,generally indicated, at I06, and thence to the motor 6. The constant.speed. unit I06 isof known construction and comprises a fiy-weightgovernor I01 provided to adjust the valve I05, the flyweights beingdriven in usual manner from engine I0 I'through gearing I10.

There. is also associated with the propeller 5 a feathering pump I08,which isdriven by electric motor I40 and is adapted to provide fluid forthe operation of, the motor 6 when blades 0 are to be moved to thefeathered position or returnedfrom that position.

The engine in nacelle IOI is under the control of. the pilot, the powerdelivered by the engine being regulated in well known manner by throttleIll, which is. adjustable by any suitable linkage, diagrammaticallyindicated at I12 (Figure 4), from lever I0 in the pilots cockpit. Thelever I0 is also connected through a suitable linkage (indicated at H0in Figure. 3) witha pinion 20I which engages a rack on a, sleeve III,the latter being axially adjusted with rotation of the pinionto vary, in.usual manner, the loading of spring I I2 to change the loading on thefiy-weight governor I01. It will be appreciated, therefore, that whenthe lever I0is adjusted theengine power is regulated. Simultaneously,the datum setting of the constant speed unit I06 is varied so that itaccords with the operating conditions of the engine selected. by thepilot: the blades 8 are moved. in known manner as the datum setting ofthe constant speed. unit is. adjusted, so thattheir pitch correspondsto. the newly selected value. of, speed.

The lever I0 is also connected by meansof alinkage, diagrammaticallyindicated at II (Figure 3) with a switch, the arm of which is shown atI2.

The lever I is movable along a slot I3 from one end I4, corresponding toslow running of the engine, to the end I which corresponds to fullpower. The lever I0 may also pass through a gate I6 and into a slot I!and be thereafter moved towards the end I'll-which also corresponds tothe full power of the engine. In passing through gate I6 from slot I3 toslot I! the lever I0 adjusts the switch I2 through linkage II so thatthe arm is set on the studs I9, 20. Similarly, when the lever is movedthrough the gate in the opposite direction the arm I2 is moved on tostud 2| for other movements of lever I0 the switch arm is not adjustedin any way.

Whilst lever I0 is in the slot I 3 the blades 8 are in the positivepitch-range so that the thrust is applied to propel the aeroplaneforwardly. When the lever I0 is in the slot I! the blades 8 are setwithin the negative pitch-range and the propeller thrust is applied as abraking force to the aeroplane.

The pump I04 of the unit I06 draws oil from the lubricating system ofthe engine and, besides supplying the motor 6 through the valve I05 itpasses oil to the valves diagrammatically indicated at 22, 23 and 24.Thus, valve 22 is supplied through channels I55, I56 and valves 23 and24 through channels I55, I51 and I58. The valve 22 regulates the passageof the pressure fluid along channel I59 to a motor I I3 associated witha relief valve II 4 which is provided on the delivery side of pump I04along channel I60. The valve 23 regulates the passage of fluid from pumpI04 along channel I60 to a motor II5 associated with the constant speedunit so as to override it in a manner later described. The valve 24regulates the passage of pressure fluid along channel I6I to a motor II6which is provided to adjust a two-position valve III.

When motor I I5 is brought into operation the unit is overriden in itsoperation. Accordingly, for convenience, this motor will be referred toas the overriding motor, valve 23 as the overriding valve and a solenoid25 which controls the operation of the valve 23 will be called theoverriding solenoid. Valve III is only brought into operation when it isdesired to move the blades from one pitch range to the other duringreversing or unreversing of the blades 8. Accordingly, motor II6 will bereferred to, for convenience, as the reversing motor, its valve 24 asthe reversing valve and a solenoid 26 which is provided to adjust thevalve as the reversing solenoid. The valve 22 regulates the passage ofpressure fluid to relief valve II4 so as to increase the pressure atwhich it operates and accordingly the valve 22 and its actuatingsolenoid 21 will be referred to as the pressure-increasing valve andsolenoid respectively.

The reversing valve 24 is normally spring urged to a position at whichvalve III is set so that pitch adjustments are performed (under thecontrol of the constant speed unit) in the positivepitch range.

Carried by ram I of pitch-change motor 6 are a pair of shoulders 28 and29 which are so arranged that, as ram I moves to the left (Figure 2) tobring the blades 0 from the positive pitchrange to the negativepitch-range, shoulder 28 engages abutment II8 when the blades haveassumed a position hereinafter referred to as the fine-pitch position.The ram I is again stopped, when stop 29 engages stop II8, with the 4blades at zero pitch. Stop H8 is removable to allow the ram to move tothe left after the stop is engaged by shoulders 28, 29. Thus, the ram isbrought into and adjusted in the negative pitch range.

The stop H8 is moved clear of shoulders 20, 29 in the following way:

When pressure fluid is delivered by pump I04 to motor 6 by pipe II9 tomove the ram 1 to the left it also passes by duct I20 to valve I2I. Thelatter is urged by spring I 22 to the right (Figure 2). The normal fluidpressure on valve I2I is incapable of moving it against spring I22. Whenshoulder 28 or 29 engages stop H8 and ram I is brought to rest, thecontinued delivery by pump I04 raises the pressure in motor 6-and, thuson valve I2I. When the pressure reaches a predetermined value valve I2Iis moved to the left due to the pressure in motor 6 acting thereon andduct I20 communicates with duct I23 and acts on piston I24. This pistonis then moved to the right against spring I25 and shoulder I26 is movedfrom under stop I I8. The latter comprises a plurality ofcircumferentially spaced spring fingers I2I which tend to contractinwardly but are prevented from so doing by shoulder I26. When theshoulder is moved clear of abutment I I8 the fingers contract and carrythe stop away from shoulders 28 or 29. When the ram is thus permitted tocontinue its travel to the left the resultant pressure fall resets valveI2I and piston I24 to the position shown in Figure 2. In this way afterstop H3 is cleared from shoulder 28 it will be automatically re-set toengage shoulder 29.

The increased pressure required to remove abutment II8 will be reachedas the blow-off pressure of relief valve II4 is made greater as laterdescribed. The arrangement of shoulders 28, 29 and stop II8 are wellknown and will not, therefore, be described in greater detail.

There is associated with the blades 8 a pitchfollowing mechanism,generally indicated at 30, and comprising a pin 3I carried by the rootof a blade, a rod 32 and a plate 33 carried by the rod. The pin 3| androd 32 are normally spaced apart (at I21) so that the mechanism has alost-motion effect and it is arranged that slightly before the bladesreach their fine-pitch setting the pin 3| will have been moved to engagerod 32 to move the plate 33 against a pair of contacts 34, 35. Thiscould occur, for instance, at +10 pitch setting. The plate 33 is ofconducting material and completes a circuit through the contacts 34, 35.

Similarly, with the continued movement of the blades 8 towards thenegative-pitch range at about +5 the plate 33 engages contact 36 therebycompleting a circuit through contacts 34 and 36: finally at about 5 theplate engages contact 3! thereby completing a circuit through thecontacts 34, 31.

Generally, the function of the mechanism described is that when thelever I0 is moved from the slot I3 into the slot H the switch arm I2 isbrought to engage contacts I6, 20. As a consequence the solenoids 25, 26and 2! are energised in a selected manner thereby (i) to bring the ram 1successively against the shoulders 28, 29, (ii) to enable the pressurefluid passing to the motor 6 to be increased so as to remove said stopsautomatically, (iii) to override the constant speed unit I06 so that theblades are moved from the positive pitch-range to the negativepitch-range and (iv) to reverse the flow of pressure fluid from valveI05 to motor 6 so that when the blades are in the negative pitch-mangethe constant speed unit I05 will be effective suitably to adjust theblades in the required sense.

It is considered desirable that this sequence of operations justoutlined be prevented from taking place until such time as the aeroplanehas touched down since it is only during the landing run and formanoeuvring on the ground generally that the braking force is required.To this end, there is provided a switch 38 (see also Figure 1) which isclosed when the undercarriage legs I03, I04 are telescoped, as occurswhen the aeroplane touches down on landing. The switch 38 is in serieswith the aeroplane battery 39 and with the solenoids 25,, 26, 21 so thatuntil the switch 38 has been closed as indicated no circuit may becompleted from the battery 39 to any of the solenoids.

The sequence of operations performed under different flight conditionswill now be described.

It will be assumed that the aeroplane is airborne and the sequence ofoperations which take place as the landing approach is made, as themachine touches down, as the braking effect is obtained by moving theblades to the negative pitch-range, as the unbraking operation isperformed, as starting of the engine from rest takes place and, finally,as the aeroplane takes-off will then be described, in that order.

Whilst the machine is flying there is of course no load on theundercarriage and the switch 38 is open. As a consequence the entirecircuit controlling the solenoids 25, 26 and 21 is dead. The propellerblades are within the positive pitchrange and are being adjustedautomatically by the constant speed unit I06, the datum setting of whichis varied by moving lever I0. The two shoulders 28 and 29 are inposition to prevent movement of the ram I, firstly, beyond fine pitchand, secondly, beyond zero pitch into the negative-pitch range.

As the landing approach is made the pilot moves the power lever I0 fromsome position along the slot I3 to the slow-running end I4 thereof. As aconsequence the datum settingof unit I 06 is adjusted and it is arrangedthat the power developed by the engine under these conditions isinsufiicient to provide the power required to drive the propeller. .As aconsequence, theapropeller windmills at the fine-pitch setting. i. .e.,ram I is against shoulder 28, to provide the remaining portion of thepower. This will havethe effect of producing drag thereby preventing thegliding speed of the aircraft from becoming excessive. If the pilotwishes to reduce this drag pleted from the battery 39, switch 30, leadI28,

switch 40 (which is normally closed) lead I29 to the solenoid 21 toenergize the latter. The pressure-increasing valve 22 is opened to applythe pressure of pump I94 to motor II3 thereby loading relief valve II4so that the pressure of fluid within the motor 6 may be increasedsufliciently to withdraw stop IIB from the fine-pitch shoulder 28against which the ram I has been brought during the landing approach(see above). As the propeller moves towards zero-pitch the plate 33 is"brought .into engagement with the .studs 34, 3 5 thereby completing acircuit from the battery, through switch 38, lead I28, lead 4| contacts34; 35, lead I30 :and a solenoid 42 so that the switch is opened and thesolenoid 21 is deenergised. This restores the normal pressure conditionsin the motor 6 so that the :stop I I8 cannot be-withdrawn from shoulder29. As a result the propeller is now free to constantspeed over :therangeof pitch settings above the zero- .pitchzshoulder 29.

When the, pilot wishes to obtain a braking thrust he moves 'power leverI0 through thegate I5 and as a-consequence switch arm I2 is moved toengage studs I9 and 20. In so doing a pair of circuits are completedfrom the battery 39 one through lead I 3| to solenoid 2S and the otherthrough lead I3 I Ito solenoid 43-.the circuits being in parallel. Whensolenoid 43 is energised, switches 44 and 45 are-closed and there iscompleted a circuit fromthe battery 39 through the studs I9, 20, leadI50, switch 44, lead I5I and switch 46 to the solenoid 25. At the sametime a circuit is completed from the battery 39 through switch 45 tosolenoid '27. As a consequence solenoids 25, 26 and 21 are now allenergised.

When the machine touches down, the switch 38 may tend to open and closewith bouncing of the undercarriageand to overcome this there isassociated with the solenoid 43 a known form of .holding circuit (notshown) which is brought into use when the solenoid is energised to.ensure thatit is maintained in this state.

When solenoids 25, 2B and 21 are energised valves 23, 24 and 22,respectively, are opened thereby applying the pressure of pump I04 tomotors I15, H6 and H3.

Operation of motor H3 loads relief valve I I4 to ensure that 'a pressurebuild-up will take place in motor 5 sufiicientto remove stop IIB fromshoulder '29 so that the blades .8 may enter the negative-pitch range.Operation of motor II5 over-rides the unit I06 toensure that thepressure fluid is delivered by pump I04 continuously in one way andoperation of motor IIB ensures that the pressureciiuid passes by duct [II No carry theblades into the negative pitch range. When the.zero-pitchshoulder 29 isremoved and the blades placed within thenegative pitchrange, plate 33 engages contact 31 at -5: contact 36 haspreviously been engaged but as this is in series with a switch 41, whichhas so far remained open, .it is not effective. When plate 33 engagescontact 31 a circuit is completed from the battery 39 through leads I28,4|, contacts 34,

31; lead I52 tosolenoid and switch 46 is opened whilst switch 41 isclosed. There is associated with the solenoid '48 a known form ofholding circuit 200which ensures that the solenoid'remains energised.

' When switch 46 is opened the overriding soleto provide that thepropeller is operating within the negative pitch-mange andis beinautomatically adjustedby unit I06 under the control of the lever 10. Thelatter is movable along slot I'I so as to vary the power of the engine.The le- (er I0 now controls to determine the braking force which isobtained.

When the aeroplane is brought to a standstill is desirable that thecontrol system be re-set prior to the engine being stopped. To this end,

=7 the lever III is moved through the gate I6 so that it is in theslow-running position I4. As a result the switch arm I2 is moved toengage the stud 2I and the circuits to the solenoids 26, 21

switch M, lead I53, switch 2I,1ead ,l32 and solenoid 25. The overridingsolenoid 25 is therefore energised and the valve 23 is set to bringmotor II5 into operation to override unit IIB so'as to move thepropeller blades into the positive pitchrange. The pressure fluid willnow pass to motor 6 by duct I33 since valve III is not being adjusted toreverse the flow. As the blades are moved the zero-pitch shoulder 29 ismoved towards its engaging position. At =+5 the plate 33 moves away fromthe contact 36 the circuit to solenoid 48 is broken, switch 41 is openedand solenoid is de-energized. The propeller is then within the positivepitch-range and i again returned to the control of the constant speedunit. The entire system is now ready for starting. The'engine may thenbe stopped.

When the engine is to be started, the lever I0 is placed at theslow-running position I4 and the engine started up. As the engine powerincreases the constant speed unit adjusts the blades 8 so that the pitchbecomes coarser. At 10 the plate 33 moves away from the contacts 34, sothat solenoid 42 becomes de-energised and consequently solenoid 21 ienergised. The fluid pressure to motor 6 is therefore at itshigher-than-normal value and holds the fine-pitch shoulder 28 in itsinoperative position so that the propeller is free to constant speedabove the zero-pitch shoulder 29, towards which it moves as the power isreduced.

From the starting position the lever I0 is moved along the slot I3towards the full power position when it is desired to take-off. As aresult the propeller speeds up and ram 1 moves to, and beyond,engagement of the fine-pitch shoulder 28 with stop H8: this stop, as hasbeen indicated above, is held inoperative until the areoplane becomesairborne whereupon the load on the undercarriage is relieved and theswitch 38 is opened. The entire electrical circuit thereupon becomesdead and the solenoid 21 is deenergised.

If desired the plate 33 and contacts 34-3I may be replaced by a pair oftwo-position switches which are operated by the rod 32 which engages aplate rotatable with the propeller. The switch arms are actuated by abell-crank lever either directly or indirectly through the agency of aslider but which, in any case, is adjusted by a slipper with movementsof the rotatable plate. The actuation of the switches -will be similarto that of the hub contacts described above.

We claim:

1. Thecombination with a variable-pitch,reversing,hydraulically-operated propeller for an aeroplane having anundercarriage and an engine to drive the propeller, of a constant-speedunit 8 to control the pitch adjustment of the blades of the propeller, asingle control to adjust, over a range, both the power output of theengine and the speed setting of the constant speed unit in the positiveand negative pitch ranges, means to over-ride the constant speed unitcomprising a valve controlled motor operatively connected to theconstant speed unit whereby the blades are moved from one pitch range tothe other, electrical means operatively associated with said valve tocontrol said over-riding means, said electrical means being actuated bythe single control at its slow-running position of the engine and switchmeans operated by the aeroplane undercarriage to render said electricalcontrol means inoperative, except when the undercarriage supports theaeroplane.

2. An engine-propeller assembly as claimed in claim 1 wherein thehydraulically-operated propeller includes a pitch-change motor andhydraulic connections between the constant-speed unit and thepitch-change motor and wherein the circuit of the electrical controlmeans incorporates switches which are actuated by the blades of thepropeller, said switches controlling hydraulic valve means whichtranspose the hydraulic connections between the constant-speed unit anda pitch-change motor of the propeller while the propeller blades are inthe negativepitch range whereby said unit automatically adjusts theblades in the negative-pitch range.

3. An engine-propeller assembly as claimed in claim 2 in which a stop isprovided normally to prevent movement of the blades to within thenegative-pitch range, said stop being displaced to allow such movementby an increase in the hydraulic pressure in the pitch-change motor to ahigher-than-normal value, means being provided to ensure that saidhigher pressure is built up when the speed-power control is suitablyadjusted after the aeroplane has landed.

4. An engine propeller assembly as claimed in claim 3 in which the meansfor over-riding the constant-speed unit, for transposing the hydraulicconnections between said unit and the pitch-change motor and forproducing the higher-than-normal hydraulic pressure is eachhydraulically controlled by the pressure fluid delivered by the pumpsupplying the pitch-change motor.

5. Anengine propeller assembly as claimed in claim 4 wherein there isprovided a hydraulic motor to adjust each of said means, a valve tocontrol the supply of pressure fluid from the pump to each said motorand a solenoid, forming part of said electrical control, for adjustingeach valve.

EDWARD HOLLINGWORTH MORRIS.

ELLIS DANVERS. THOMAS EDWARD GODDEN.

REFERENCES CITED The following references are of record in the flle ofthis patent:

UNITED STATES PATENTS Number Name Date 2,154,887 Baker Apr. 18, 19392,402,065 Martin June 11, 1946

